PostgreSQL SQL - pl/* overhead ...

Author

pl/* overhead ...

Marc G. Fournier

2005-10-27, 8:08 am

Does anyone know of, or have, any comparisions of the overhead going with
something like pl/perl or pl/php vs using pl/pgsql?

Thanks ...

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Michael Fuhr

2005-10-27, 8:08 am

On Wed, Oct 26, 2005 at 12:58:13AM -0300, Marc G. Fournier wrote:
> Does anyone know of, or have, any comparisions of the overhead going with
> something like pl/perl or pl/php vs using pl/pgsql?

Benchmark results will probably depend on the type of processing
you're doing. I'd expect PL/pgSQL to be faster at database operations
like looping through query results, and other languages to be faster
at non-database operations like text munging and number crunching,
depending on the particular language's strengths.

[Does quick test.]

Whale oil beef hooked. PL/pgSQL just outran PL/Perl when I expected
the latter to win. Hang on, let me play with it until it comes back
with the results I want....

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Michael Fuhr

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Marc G. Fournier

2005-10-27, 8:08 am

On Wed, 26 Oct 2005, Michael Fuhr wrote:

> On Wed, Oct 26, 2005 at 12:58:13AM -0300, Marc G. Fournier wrote:
>
> Benchmark results will probably depend on the type of processing
> you're doing. I'd expect PL/pgSQL to be faster at database operations
> like looping through query results, and other languages to be faster
> at non-database operations like text munging and number crunching,
> depending on the particular language's strengths.
>
> [Does quick test.]
>
> Whale oil beef hooked. PL/pgSQL just outran PL/Perl when I expected
> the latter to win. Hang on, let me play with it until it comes back
> with the results I want....

'k, let's repharase the questions :)

Overall, I'd expect pl/pgsql to have less overhead, since its "built into"
the server ... in the case of something like pl/php or pl/perl, assuming
that I don't use any external modules, is it just as 'built in', or am I
effectively calling an external interpreter each time I run that function?

For instance, if there wasn't something like to_char() (thanks for
pointing that one out), then i could write a simple pl/perl function that
'simulated it', but itself did no db queries just a simple:

RETURN sprintf("%04d", intval);

Don't know if that made much more sense ... ?

----
Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
Email: scrappy@hub.org Yahoo!: yscrappy ICQ: 7615664

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Jan Wieck

2005-10-27, 8:08 am

PL/pgSQL is as *internal* as for example PL/Tcl. The two are actually
pretty similar and I would expect them to perform similar, if one knows
what and how he does.

PL/pgSQL is an external shared object, loaded on call of the first func
per backend. Same for PL/Tcl.

PL/pgSQL takes pg_proc.prosrc and compiles all control structures (if,
else, loop) into a form of bytecode. Query strings are left alone until
the statements are actually executed. Tcl has a similar concept of
bytecode compilation.

PL/pgSQL turns all expressions and SQL statements into prepared SPI
plans. It short-circuits simple expressions by directly calling the node
execution, so it works with PostgreSQL's native types and operators.
Here is the big difference, PL/Tcl turns all datums into their external
string representations and then does the Tcl dual-ported-object munging
and math. However, if used right it also offers prepared SPI plans.

If the implementation of functionality results in widely similar code, I
would expect PL/pgSQL and PL/Tcl to perform similar. However, doing the
prepared SPI stuff in Tcl is a bit of work. OTOH doing extensive string
processing in PL/pgSQL is a nightmare. That difference should drive the
decision which language to use when.

Jan

On 10/26/2005 5:48 AM, Marc G. Fournier wrote:

> On Wed, 26 Oct 2005, Michael Fuhr wrote:
>
>
> 'k, let's repharase the questions :)
>
> Overall, I'd expect pl/pgsql to have less overhead, since its "built into"
> the server ... in the case of something like pl/php or pl/perl, assuming
> that I don't use any external modules, is it just as 'built in', or am I
> effectively calling an external interpreter each time I run that function?
>
> For instance, if there wasn't something like to_char() (thanks for
> pointing that one out), then i could write a simple pl/perl function that
> 'simulated it', but itself did no db queries just a simple:
>
> RETURN sprintf("%04d", intval);
>
> Don't know if that made much more sense ... ?
>
>
> ----
> Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
> Email: scrappy@hub.org Yahoo!: yscrappy ICQ: 7615664
>
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> TIP 3: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faq

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